One problem with known devices used to administer measured quantities of medicine, in other words dosages, such as hypodermic syringes, in particular, and also devices used to administer medicines in a pulverulent or viscous dosage form, is that they lack means which will ensure that the dispensing device can be returned quickly to its original state so that a new dosage ampoule can be fitted into the device.
The concept of the present invention can be readily applied to different known kinds of medicine dispensing devices which include a screw mechanism for reconstituting and/or metering and administering the content of a prefilled ampoule. Dispensers of this kind are well known in the art; see, for instance, U.S. Pat. No. 4,592,745.
Swedish patent specifications SE,B,465065 and SE,B,464797 (corresponding to EP,B,298067) describe dispensers in the form of hypodermic syringes which include a screw mechanism for displacing a plunger in a prefilled cylinder.
These specifications disclose how dual-chamber ampoules can be reconstituted by rotating the screw. Dispensing and administering of the medicine is then effected with the aid of an arrangement which is activated by means of an operating lever.
In order to return a syringe of this kind to its original state and therewith enable a fresh ampoule to be fitted and reconstituted and its contents dispensed, it is necessary to withdraw the screw mechanism manually back to its starting position. This is a time consuming task and may easily be neglected, which may result in damage to the screw mechanism or in an impairment in the metering accuracy of the dispenser.
Although this problem can be overcome by constructing the dispenser, or syringe, for one-time-use only, with the intention of discarding the dispenser after having emptied the ampoule with the plunger located in its forward position, this solution is not a desirable solution, mainly for material handling reasons.
Consequently, there is a need for a dispenser which includes a simple arrangement by means of which those components of the dispenser which have been active in reconstituting and/or dispensing a measured quantity of medicine, or dose, can be quickly returned to their respective starting positions after emptying the ampoule. This applies in particular to the type of hypodermic needles described above, such needles being widely used within the art.
It is particularly desirable to provide an arrangement by means of which a screw-threaded actuator or like devices, such as the screw described above for instance, is returned quickly to its starting position in which the dispenser, or syringe, can be fitted with a fresh ampoule.
Swedish published specification 379089 and FR,A1, 2613789 teach a number of technical solutions to the problem of moving such screw-like devices quickly with the intention of releasing or securing the devices without coming into contact with the screw threads thereof.
None of these publications, however, gives an indication as to how a screw-threaded actuator intended for dispensing a metered quantity of medicine from an ampoule or similar container can be returned to its original position for administering a new dosage.